1. Field of the Invention
The present invention relates to a recording head capable of performing stable printing, and to a recording apparatus adapted to perform recording using the recording head.
2. Description of the Related Art
Various recording heads have been known, on which a plurality of recording elements are arranged in a line or in a plurality of lines. In the recording head of such a kind, several or tens of drive integrated circuits, each of which can simultaneously drive N recording elements as one block, are mounted on the same substrate. Among such recording heads, a recording head including a plurality of electrothermal conversion elements as recording elements, which generate discharge energy used to discharge ink from a discharge port, has been known. Some of such a recording head drives a large number of recording elements and needs a large amount of electric power to drive the recording elements. Additionally, in a case where such a recording head continuously drives a recording element, heat is stored therein to change a recording density. Also, the recording element is affected by heat of an adjacent recording element.
Thus, the following methods have been proposed. One is a method of dividing recording elements into a plurality of blocks, and performing a sequential driving operation of a plurality of recording elements adjoining one another in each of the blocks. Another is a method of dividing recording elements into a plurality of blocks, and performing a distributed driving operation of simultaneously driving a plurality of recording elements positioned relatively distant from one another in each of the blocks.
Meanwhile, in a case where adjacent recording elements are simultaneously driven in an inkjet recording apparatus, nozzles sometimes interfere with one another by mutual pressures generated at ink discharge. This pressure interference (i.e., crosstalk) may cause change in the recording density. Thus, preferably, after a recording element is driven, an idle period is provided to prevent heat dissipation or crosstalk.
To this end, the method of performing the distributed driving operation is effective, especially, in a case where the recording elements to be simultaneously driven are distributed in a columnwise direction. According to this method, the adjacent recording elements are not simultaneously driven. Thus, influence on each recording element from adjacent recording elements can be eliminated by providing the idle period. More specifically, the distributed driving operation is achieved by a plurality of enable terminals connected in common to all the recording elements that can simultaneously be driven. FIG. 7 illustrates a conventional recording element drive circuit of a recording head. Japanese Patent Application Laid-Open No. 7-68761 discusses a similar circuit.
The driving method of the conventional circuit is herein now described. First, an image data transfer clock is transferred from a clock terminal CLK to a shift register circuit 10. Also, image data is transferred from a data signal terminal DATA to the shift register circuit 10. To cause a latch circuit 11 to latch image data, a latch pulse signal is input from a latch terminal LAT. Also, image data are aligned corresponding to the recording elements. In one period of the latch pulse signal, the recording elements can be energized according to the image data in each of blocks. Time-divisional driving is performed on the recording elements in units of blocks. A decoder decodes data representing combinations of on-levels and off-levels of signals ENB_0, ENB_1, ENB_2, and ENB_3 into data respectively representing 16 blocks. Thus, the blocks can be selected. In the period of the latch pulse signal, the blocks are sequentially selected. In a time period corresponding to each of 16 blocks, pulse width regulating signals respectively corresponding to 16 blocks are input from heat enable terminals HEAT_1 and HEAT_2. Consequently, a time-divisional distributed driving operation can be achieved by setting a time-division number at 32. The driving pulse signal applied to each of the recording elements has a pulse width set so that a rise time and a fall time of a functional element (i.e., a driver) 3 are short enough to enable high-resolution control.
However, in a case where the recording head of the above configuration is used to achieve high-speed image formation, high-resolution color image formation, and recording-head miniaturization, the following problems sometimes occur. In increasing the number of recording elements to achieve high-speed image formation and high-resolution color image formation, the number of blocks to be time-divisionally driven or the number of recording elements to be simultaneously driven may increase. However, to achieve high-speed image formation, there is a limit to increase in the number of blocks. Thus, there is a growing tendency towards increase in the number of recording elements to be simultaneously driven.
However, an increase in the number of recording elements to be simultaneously driven results in occurrence of a problem due to recording current concentration in wires. This problem is a malfunction due to switching noises generated at a rise and a fall of a driving pulse signal. For example, in a case where the rise time or the fall time t of the function element 3 is 100 nanoseconds, where self-inductance of the wire is 100 nanohenries, and where a concentrated current flowing in the wire is 1 ampere, an induced voltage V (volts) is calculated as follows:V=L·(di/dt)=100×10−9×1/100×10−9×1=1 (volt).
That is, an induced voltage of 1V is generated as a noise voltage. This noise voltage largely affects a COMS (complementary metal-oxide) or TTL (transistor-transistor logic) logic gate circuit unit. Especially, in a case where the logic gate circuit unit is a CMOS logic circuit having an operating voltage of 3.3V or less, this level of the noise voltage substantially reaches a threshold level. Thus, sometimes, a malfunction occurs in a recording head device including both a control block, which has the function element 3 adapted to switch a large current, and a COMS or TTL logic gate circuit unit constituting the shift register and the latch circuit.
The switching noise at the simultaneous driving has hitherto been a problem. Thus, several countermeasures against the switching noise have been known. For example, a method of stepwise delaying driving pulse signals applied to recording elements to be driven as recording-elements of the same block has been known. According to this method, a delay element is configured to stepwise delay timing, with which a driving pulse signal is applied to each of the recording elements, according to a pulse width regulating signal in view of a level and a width of a switching noise.
However, this method encounters the following problem in a case where the number of recording elements driven in a driving period of 1 block is further increased. That is, although an allowable pulse width time is usually allotted to each of the recording elements so that all the recording elements can be driven in a driving period (i.e., a period in which 1 recording element is continuously driven), a sufficient delay time cannot be taken. Consequently, it is difficult to prevent the switching noise from adversely affecting the recording head.